Two-dimensional Int array in Kotlin

Question

Is it the easiest way to declare two-dimensional Int array with specified size in Kotlin?

val board = Array(n, { IntArray(n) })

this.data = Array(rowCount) { IntArray(colCount) } the semantic changed — prof_FL
– prof_FL, Commented Jan 17, 2022 at 14:29

3 revs, 2 users 74% · Accepted Answer · 2016-10-03 14:09:40Z

22

Here are source code for new top-level functions to create 2D arrays. When Kotlin is missing something, extend it. Then add YouTrack issues for things you want to suggest and track the status. Although in this case they aren't much shorter than above, at least provides a more obvious naming for what is happening.

public inline fun <reified INNER> array2d(sizeOuter: Int, sizeInner: Int, noinline innerInit: (Int)->INNER): Array<Array<INNER>> 
    = Array(sizeOuter) { Array<INNER>(sizeInner, innerInit) }
public fun array2dOfInt(sizeOuter: Int, sizeInner: Int): Array<IntArray> 
    = Array(sizeOuter) { IntArray(sizeInner) }
public fun array2dOfLong(sizeOuter: Int, sizeInner: Int): Array<LongArray> 
    = Array(sizeOuter) { LongArray(sizeInner) }
public fun array2dOfByte(sizeOuter: Int, sizeInner: Int): Array<ByteArray> 
    = Array(sizeOuter) { ByteArray(sizeInner) }
public fun array2dOfChar(sizeOuter: Int, sizeInner: Int): Array<CharArray> 
    = Array(sizeOuter) { CharArray(sizeInner) }
public fun array2dOfBoolean(sizeOuter: Int, sizeInner: Int): Array<BooleanArray> 
    = Array(sizeOuter) { BooleanArray(sizeInner) }

And usage:

public fun foo() {
    val someArray = array2d<String?>(100, 10) { null }
    val intArray = array2dOfInt(100, 200)
}

edited Oct 3, 2016 at 14:09

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3 revs, 2 users 74%
Jayson Minard

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4 Comments

Michele d'Amico Over a year ago

Can you give some documentation's links? I can found any reference and Idea kotlin plug in seams do not resolve it.

Jayson Minard Over a year ago

The functions and their source code are in my answer @Micheled'Amico ... they are not part of the stdlib.

Michele d'Amico Over a year ago

Sorry I was too lazy when I reed your answer. .... But I tried it and generic version doesn't work. Even it seams correct and it should return a Array(Array<Something>) at run time I receive java.lang.ClassCastException: [[Ljava.lang.Object; cannot be cast to [[Something; exception. Moreover IMHO a better signature can be array2d(sizeOuter: Int, sizeInner: Int, init: (Int, Int)->INNER). I'll file a question to understand what is wrong your function definition.

Michele d'Amico Over a year ago

You already meet this issue at stackoverflow.com/q/34514861/4101725 ... I open a issue on You Track youtrack.jetbrains.com/issue/KT-10555

Andrey Breslav · Accepted Answer · 2014-12-17 14:59:41Z

12

Currently this is the easiest way, we will extend the standard library with appropriate functions later

answered Dec 17, 2014 at 14:59

Andrey Breslav

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3 Comments

Ryan Over a year ago

Do I have other methods to declare two-dimensional Int array Now?

thuanle Over a year ago

It's 1.1.3 now. Does it up to date?

Alexander Ites Over a year ago

Are there any new methods to declare two-dimensional Int array available in 2024?

Avijit Karmakar · Accepted Answer · 2017-07-20 04:12:53Z

2

Yes, your given code is the easiest way to declare a two-dimensional array.

Below, I am giving you an example of 2D array initialization & printing.

fun main(args : Array<String>) {
    var num = 100

    // Array Initialization
    var twoDArray = Array(4, {IntArray(3)})
    for(i in 0..twoDArray.size - 1) {
        var rowArray = IntArray(3)
        for(j in 0..rowArray.size - 1) {
            rowArray[j] = num++
        }
        twoDArray[i] = rowArray
    }

    // Array Value Printing
    for(row in twoDArray) {
        for(j in row) {
            print(j)
            print(" ")
        }
        println("")
    }

}

answered Jul 20, 2017 at 4:12

Avijit Karmakar

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1 Comment

androidguy Over a year ago

But you don't need var rowArray = IntArray(3). Because the second parameter of Array(...) initializes each array element. So you could do val rowArray = twoDArray[i].

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